Johnson Matchbox Design
Bill Russell
opinon is that the Johnson Matchbox is the best matchbox ever
made...with a few exceptions. If this is true, why hasnt anyone made a
matchbox using the same components and design as Johnson did. The
function of a tuner for use with balanced lines seems to be the
downfall of most new tuners usually because of the transformer used to
balance the output. Cant anyone duplicate Johnsons design???
Bill KC2IFR
Dan Richardson
<wi...@global2000.net> wrote:
Bill,
Check LB's wrtie up on his web page at: http://www.cebik.com/link.html
I think it will answer many of your questions.
73
Danny, K6MHE
Edward A. Feustel
really designed for long-wire and balanced lines of up to 1000 ohms.
Note that there is no coaxial output on the MB.
The majority of use today is 50 ohm unbalanced to the antenna and the
tuner is not designed for that.
If you want a balanced tuner, the Palstar Balanced Tuner or the Bliss
Balanced tuner would appear to be the way to go and match a broader
range
than the matchbox. If you want an unbalanced wide range tuner, you want
something like a Ten Tec 238.
One final note, the thing that makes the MB is the dual differential
capacitor.
I don't know of anyone except Johnson who made these special purpose
capacitors.
Ed, N5EI
Tom W8JI
<efeu...@ists.dartmouth.edu> wrote:
>The matchbox has a limited range of matching impedances and was
>really designed for long-wire and balanced lines of up to 1000 ohms.
>Note that there is no coaxial output on the MB.
True enough, except my KW Matchboxes have coaxial outouts
>If you want a balanced tuner, the Palstar Balanced Tuner or the Bliss
>Balanced tuner would appear to be the way to go and match a broader
>range
Actually moving the balun to the input does NOT improve balance or
matching range. The Bliss tuner is in a formica cabinet, and does not
look well engineered. My calculations show it will not match
impedances below ~30 ohms on 160 meters.
>than the matchbox. If you want an unbalanced wide range tuner, you want
>something like a Ten Tec 238.
Almost any C-L-C T network tuner will have a wide matching range.
73 Tom
Ron McConnell
> If you want a balanced tuner, ...
> Palstar Balanced Tuner or the Bliss Balanced tuner
Ah! New ones on me.
Where do you find those? Web site?
Specs? US$? etc.?
73,
Ron McConnell
w2...@arrl.net
CAM
> Cant anyone duplicate Johnsons design???
Not for a price that hams are willing to pay. If you feed
your antenna system at a current maximum point, virtually
all of the balun design problems disappear.
--
cheers, CAM
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Tom W8JI
wrote:
>"Edward A. Feustel" = Ed, N5EI, wrote:
>
>> If you want a balanced tuner, ...
>
>> Palstar Balanced Tuner or the Bliss Balanced tuner
>
>Ah! New ones on me.
>Where do you find those? Web site?
>Specs? US$? etc.?
I tried to find some specs, but couldn't. I wound up modelling it
based onn the description of components.
Actually, it sounds and looks pretty "homebrew" as far as "design"
goes. I noticed it is a "formica" cabinet and has an off-the-shelf SWR
meter installed in a cutout, and I think I saw a big knife switch.
The components they use certainly won't allow matching a low impedance
on the lower frequencies.
What strikes me most is they seem to think moving the balun to the
input makes the balun work better, but read carefully and judge for
yourself.
73 Tom
Tom W8JI
wrote:
>Not for a price that hams are willing to pay. If you feed
>your antenna system at a current maximum point, virtually
>all of the balun design problems disappear.
Common mode impedance has nothing to do with differential mode
impedance.
You can have the same or worse problems feeding at a current point as
at a voltage point.
73 Tom
CAM
> CAM <Cecil....@IEEE.org> wrote:
>>Not for a price that hams are willing to pay. If you feed
>>your antenna system at a current maximum point, virtually
>>all of the balun design problems disappear.
>
> Common mode impedance has nothing to do with differential mode
> impedance.
Nothing? Are you saying that the common-mode current will be
same for a 1:1 balun with a choking impedance of 500 ohms that
sees either a 50 ohm dummy load or a 5000 ohm dummy load? Did
they repeal Ohm's law while I wasn't looking?
avatar
version.
2. I built a CLC T-tuner with a 1:1 voltage balun at the input which works
well.
3. There are some variable caps that can be easily change to provide
differential tuning. Any dual section variable that uses spacers between the
rotor plates is a candidate. These usually have a nut on the rear end of the
shaft. By loosening the nut enough to relieve pressure on the plate spacers
you can move the plates. This only has to be done on one of the two
sections.
Dave
W0MAY
Bart Rowlett
CAM wrote:
>
> Tom W8JI wrote:
>
> > CAM <Cecil....@IEEE.org> wrote:
> >>Not for a price that hams are willing to pay. If you feed
> >>your antenna system at a current maximum point, virtually
> >>all of the balun design problems disappear.
> >
> > Common mode impedance has nothing to do with differential mode
> > impedance.
>
> Nothing? Are you saying that the common-mode current will be
> same for a 1:1 balun with a choking impedance of 500 ohms that
> sees either a 50 ohm dummy load or a 5000 ohm dummy load?
Yes. Common mode current has little to do with the differential mode
load impedance.
bart
wb6hqk
Earl Andrews
there that follows the design somewhat..I saw it on a web site with
schematics etc. Not sure when or if it is still produced.
Too bad someone woulnt build a clone of this unit and
perhaps some of the old popular radios! ie ten tec argonaut ect.
73 Earl VE3AB
Tom W8JI
>
>I have no judgment over the two mentioned brands, but the principle is to
>isolate the tuning circuit completely from the input.
No matter what end of the network you do that on, common mode voltage
and impedance remains the unless you are using a balanced network with
a ground in the center of the network.
The simple "trick" of using a choke on the input and a flopating
network does virtually nothing to change common mode voltage across
the choke balun.
>The transformer is working on 50 Ohm which can be constructed over a wide
>frequency range. I made a 50:50 ohm 100W transformer with swr 1:1.5 over 10-160
>meter. The swr error can be compensated to 1:1 exactly (50 ohm) by offering a
>slightly different than 50 ohm impedance at the tuning circuit side of the
>transformer. Put the swr meter at the input (primary) and you will not even
>notice it. Stray capacitance between prim & sec is 10 pf.
Are you using an isolated primary and secondary transformer? Virtually
all tuners using the "balun on the input scheme" use conventional
choke baluns.
>Behind the transformer any well performing asymmetric tuning circuit can be
>used, L or T. The impedance range of the tuner depends on the performance of
>this circuit, not on the transformer.
>I did not try to make a transformer for hi power but guess this is possible.
It would probably be very difficult to make a broad-band high-power
1:1 ratio isolation transformer with low primary to secondary
isolation, because of core losses and the size of the transformer.
Also, you can get into trouble quick with some networks on higher
bands because the series impedance of the network might be the
opposite sign of the reactance in the choke or isolation transformer.
By the time we are done with all that fussing around, we might as well
buiild a good choke balun and put it on the output.
My point is the advantage of moving baluns to the input is oversold.
In most systems with most baluns, it doesn't mean a thing.
73 Tom
Tom W8JI
wrote:
>Tom W8JI wrote:
>
>> CAM <Cecil....@IEEE.org> wrote:
>>>Not for a price that hams are willing to pay. If you feed
>>>your antenna system at a current maximum point, virtually
>>>all of the balun design problems disappear.
>>
>> Common mode impedance has nothing to do with differential mode
>> impedance.
>
>Nothing? Are you saying that the common-mode current will be
>same for a 1:1 balun with a choking impedance of 500 ohms that
>sees either a 50 ohm dummy load or a 5000 ohm dummy load? Did
>they repeal Ohm's law while I wasn't looking?
No, but they developed circuit theory at some point.;-)
For example, the common-mode impedance of a very small series-resonant
loop antenna is very high, and capacitive. The differential mode
impedance is very very low. Add a typical choke balun and common mode
current increases!
Dipoles viewed at the end of a feeder will vary all over the place
between the common mode and differential mode impedances, because the
velocity factor and impedance of the feeder is different in common
mode than it is in differential mode. There are many cases where
adding a 500 ohm inductive reactance balun will make the unbalance get
worse than not having any balun at all, even when fed at a current
point.
While we can find cases that somewhat track, in most applications
there will be quite a difference in the behavior. Feeding at a current
point does not guarantee anything, except the differential impedance.
73 Tom
Tom W8JI
wrote:
>I have a Johnsons Matchbox and I think there may be a German unit out
>there that follows the design somewhat..I saw it on a web site with
>schematics etc. Not sure when or if it is still produced.
>Too bad someone woulnt build a clone of this unit and
>perhaps some of the old popular radios! ie ten tec argonaut ect.
It would be mostly for nostalgia Earl. All my KW matchboxes are tucked
away in the barn, because conventional T networks with baluns
actually work better.
73 Tom
CAM
>
> CAM wrote:
>>Are you saying that the common-mode current will be
>>same for a 1:1 balun with a choking impedance of 500 ohms that
>>sees either a 50 ohm dummy load or a 5000 ohm dummy load?
>
> Yes. Common mode current has little to do with the differential mode
> load impedance.
So the stuff in "Baluns: What They Do And How They Do It" is wrong?
CAM
>>Tom W8JI wrote:
>>>Common mode impedance has nothing to do with differential mode
>>>impedance.
> While we can find cases that somewhat track, in most applications
> there will be quite a difference in the behavior. Feeding at a current
> point does not guarantee anything, except the differential impedance.
Are you saying we can find cases where common-mode current does
have some relationship to differential currents. That contradicts
what you said before.
Given a balanced system with balanced currents, I believe the
misuse of a balun can *cause* considerable common-mode currents
where those same currents would be negligible with a link-coupled
balanced tuner. I think that is what is asserted in "Baluns: What
They Do And How They Do It".
Tom W8JI
wrote:
>Are you saying we can find cases where common-mode current does
>have some relationship to differential currents. That contradicts
>what you said before.
It doesn't contradict anything I said. The two modes are independent
modes. Being independent, they can be the same, they can be different.
The statement "feeding at a current point" solves or reduces
"problems" is no more correct than the silly notion that placing a
balun at the input of a floating matching network somehow makes a
better balanced tuner.
>Given a balanced system with balanced currents, I believe the
>misuse of a balun can *cause* considerable common-mode currents
>where those same currents would be negligible with a link-coupled
>balanced tuner. I think that is what is asserted in "Baluns: What
>They Do And How They Do It".
A link in the wrong situation can increase common mode currents on a
line, just as a balun in the wrong situation can increase common mode
currents. We have to look at the exact situation.
73 Tom
Jan on4caf
On Sat, 22 Sep 2001 00:10:05 GMT, 2w...@contesting.com (Tom W8JI) wrote:
>On Sat, 22 Sep 2001 00:55:37 +0200, jan....@pi.be (Jan on4caf)
>>
>>I have no judgment over the two mentioned brands, but the principle is to
>>isolate the tuning circuit completely from the input.
>
>No matter what end of the network you do that on, common mode voltage
>and impedance remains the unless you are using a balanced network with
>a ground in the center of the network.
>
>The simple "trick" of using a choke on the input and a flopating
>network does virtually nothing to change common mode voltage across
>the choke balun.
I agree
>>The transformer is working on 50 Ohm which can be constructed over a wide
>>frequency range. I made a 50:50 ohm 100W transformer with swr 1:1.5 over 10-160
>>meter. The swr error can be compensated to 1:1 exactly (50 ohm) by offering a
>>slightly different than 50 ohm impedance at the tuning circuit side of the
>>transformer. Put the swr meter at the input (primary) and you will not even
>>notice it. Stray capacitance between prim & sec is 10 pf.
>
>Are you using an isolated primary and secondary transformer?
Yes
>Virtually
>all tuners using the "balun on the input scheme" use conventional
>choke baluns.
On the web site of one of the above mentioned tuners they talk about a
"transformer" so I guessed they meant a transformer but I'm not sure.
>>Behind the transformer any well performing asymmetric tuning circuit can be
>>used, L or T. The impedance range of the tuner depends on the performance of
>>this circuit, not on the transformer.
>>I did not try to make a transformer for hi power but guess this is possible.
>
>It would probably be very difficult to make a broad-band high-power
>1:1 ratio isolation transformer with low primary to secondary
>isolation, because of core losses and the size of the transformer.
The 100W all band version is only 2". On 100W and 50 Ohm no core heating is
noticeable, did not test it on higher power.
>Also, you can get into trouble quick with some networks on higher
>bands because the series impedance of the network might be the
>opposite sign of the reactance in the choke or isolation transformer.
transformer, not choke.
This can be partially compensated by caps over the windings.
I have put measurements I did last year on a web page:
http://www.qsl.net/on4caf/Web/measurements.htm
This is an example of a 100W transformer for 10-160 meters,
160 meter is a bit on the edge but still good usable.
For high power the same principle can be used using two but with smaller band
width switched over the frequency range.
>By the time we are done with all that fussing around, we might as well
>buiild a good choke balun and put it on the output.
Cannot really judge because I never did measurements on such an output balun but
my feeling tells me that on some situations the influence of the balun can be
disturbing and even give considerable losses and asymmetry. ( low Z and high
reactive loads or on High Z/High reactive load's?)
>My point is the advantage of moving baluns to the input is oversold.
>In most systems with most baluns, it doesn't mean a thing.
Baluns yes, transformers, don't think so.
Best 73,
Jan Anker, on4caf
Peter O. Brackett
Like the story of the blind men exploring the elephant, you are both right.
In every system there are common modes [a.k.a. longitudinal modes] and there
are differential modes [a.k.a. metallic modes].
Common modes and differential modes may be coupled to each other, but then
again they may not be coupled to each other.
All practical systems have differential mode inputs [dmi] and differential
mode outputs [dmo], what many practicioners ignore is that they also have
common mode inputs [cmi] and common mode outputs [cmo]. And further... what
many more practicioners ignore is that these modes may in fact be
cross-coupled!
Often in practice the common modes and the differential modes are
"cross-coupled" by coupling impedances or "coupling modes" which cannot
always be ignored. If these mode cross-coupling impedances are not
infinite, or the associated mode cross-transfer functions are not zero, then
the common and differential modes cannot be treated as independent systems.
If the common modes are completely unobservable and uncontrollable from the
differential modes and vice versa then, and only then, are the mode
sub-systems independent. The degree of mode coupling is a function of the
levels of the mode cross-coupling impedances/transfer functions.
The degree of cross-coupling, often rated in dB as a function of frequency,
can be quantified and measured by the common mode rejection ratio [CMRR],
which measures the degree of coupling from the common mode to the
differential mode, and by the differential mode rejection ratio [DMRR] which
measures the degree of coupling in the reverse direction.
From a transfer function viewpoint it's useful to view all systems as
potentially having four transfer functions Td, Tc, Tcd, and Tdc defined as
follows:
dmo/dmi = Td
cmo/cmi = Tc
dmo/cmi = Tcd [Inverse of the common mode rejection ratio]
cmo/dmi = Tdc [Inverse of the differential mode rejection ratio]
Viewed explicitly in this way, everthing becomes clear, the conceptual
difficulty that always arises in practice is that in most practical systems,
Tc, Tcd and Tdc are assumed to be zero. In fact the cross-coupling
transfers Tcd and Tdc are usually caused by parasitic or unwanted stray
impedances over which the designer and analyzer often has little or no
control!
And most often designers and analyzers of systems refuse to visualize ot
take into account quantatively the presence of the mode cross-coupling
impedances. These impedances don't ever appear on the schematic diagrams.
Therefore they are not there! Heh, heh.
It seems that there are three levels of expertise in this esoteric part of
the analog art domain.
(1) Novices consider only Td. Cuz Td is on the schematic and bill of
material.
(2) Smart folks consider both Td and Tc. Tc is never on the schematic and
bill of material, but it must be considered in precise systems.
(3) The really savvy are the ones who know and deal with Tdc and Tcd in
order to understand and fix problems caused by the unwanted Tc.
BTW... no where do I see any material that "teaches" this material at
levels (2) and (3)...
And that my friends IMHO.... is the largest part of the "magic" of analog
design. Magic in the sense of Wireless World's Arthur C. Clarke.
Let's keep levels (2) and (3) out of the hands of the unwary!!
I ask, is this a conspiracy?
It seems that, like myself, every generation of "electricians" has to learn
this "theory" from the school of hard knocks. In school they taught me
about Td, then I was thrown to the wolves and tried to make a living, and I
had to learn about Tc the hard way, then I learned about Tdc and Tcd to be
able to measure and deal with what I learned about Tc.
I believe that's why "true analog designers" [the really savvy??] will never
be without work.
True analog desingners, know how to deal with items that are not on the
schematic diagram or bill of materials.
Sorry for the ramble, just some thoughts...
Comments, thoughts?
--Peter K1PO
"Tom W8JI" <2w...@contesting.com> wrote in message
news:3bac84c9....@news.akorn.net...
Richard Clark
<ab...@ix.netcom.com> wrote:
>
>(1) Novices consider only Td. Cuz Td is on the schematic and bill of
>material.
>(2) Smart folks consider both Td and Tc. Tc is never on the schematic and
>bill of material, but it must be considered in precise systems.
>(3) The really savvy are the ones who know and deal with Tdc and Tcd in
>order to understand and fix problems caused by the unwanted Tc.
>
>BTW... no where do I see any material that "teaches" this material at
>levels (2) and (3)...
>
snip
>
>True analog desingners, know how to deal with items that are not on the
>schematic diagram or bill of materials.
>
>Sorry for the ramble, just some thoughts...
>
>Comments, thoughts?
>
>--Peter K1PO
>
Hi Peter,
Being one of those analog designers, I long (20 years) ago found
references to this problem (common modalities) when I approached the
job of designing the flight data recorder for the 757/767 generation
of aircraft.
Consider:
"Noise Reduction Techniques in Electronic Systems," Henry W. Ott
or
"Grounding and Shielding Techniques in Instrumentation," Ralph
Morrison.
Neither book is thicker than an inch, in fact Morrison's tome weighs
in at 144 pages cover to cover. However in those same 144 pages is
the most complete and comprehensive coverage through illustration of
every conceivable interface between circuits. As far as I am
concerned, Ralph Morrison has no equal on the subject (level 4).
Other recommended titles:
"Noise in Measurements," Aldert van der Ziel
"Low-Noise Electronic Design," C.D. Motchenbacher & F.C. Fitchen
73's
Richard Clark, KB7QHC
George, W5YR
My first job out of grad school in 1957 was to help design and build Texas
Instruments' first digital computer - 3500 vacuum tubes worth! We did it
with a team of only four engineers so we all got a pretty good look at all
aspects of the system.
In dealing with digital logic - for the first time in my limited experience
at that time - I soon became convinced that the difficulties lay not in the
digital end of things - that was straightforward and obeyed the rules! -
but rather that all our problems came from the *analog* aspects of digital
circuit design and operation. Once, as designers, we recognized this truth
of Nature and applied ourselves accordingly, we got on with the project and
ended up with a winner that earned its keep for over 10 years doing mostly
government contract data processing.
To this day, I have been impressed that while our world of integrated
circuits has removed many of the problems we faced in those innocent days,
I suspect that it is still the analog aspects of undesired circuit
coupling, parasitic system elements, unintended or unsuspected
transmission-line effects, etc. etc. that continue to make life difficult
for the digital designer.
So, I fully concur with your paragraph quoted below on the basis of several
decades in this game.
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
George, W5YR
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
Peter O. Brackett
Thanks for those references.
BTW... Present company excepted [Youngsters like you and me Richard! Heh,
heh.] I've found that those references are not widely known by the current
generation of younger engineers.
What University/College teaching EE, or CE, or CS at undergradutate [or
gradutate level] uses those references in any of it's curriculum classes?
Where does that subject appear on any ABET approved curriculum?
Can you name any? How many of today's University/College faculty have
these references on their bookshelf?
I am worried about this since many of our bright younger engineers and
technicians arriving in industry in the last few years [a generation or so ~
15-20 years] are completely in the dark about this stuff. Shame...
Best,
--Peter K1PO
"Richard Clark" <kb7...@home.com> wrote in message
news:lmkpqtovdnd03lnu2...@4ax.com...
Peter O. Brackett
[snip]
"George, W5YR" <w5...@att.net> wrote in message
news:3BACEF49...@att.net...
> Familiar words, Peter.
>
> My first job out of grad school in 1957 was to help design and build Texas
> Instruments' first digital computer - 3500 vacuum tubes worth! We did it
> with a team of only four engineers so we all got a pretty good look at all
> aspects of the system.
>
> In dealing with digital logic - for the first time in my limited
experience
> at that time - I soon became convinced that the difficulties lay not in
the
> digital end of things - that was straightforward and obeyed the rules! -
> but rather that all our problems came from the *analog* aspects of digital
> circuit design and operation. Once, as designers, we recognized this truth
> of Nature and applied ourselves accordingly, we got on with the project
and
> ended up with a winner that earned its keep for over 10 years doing mostly
> government contract data processing
[snip]
Heh, heh... thanks for the comments George, I believe that it's simply a
question of who Rules.
Differential equations or difference equations?
Differential equations Rule!
Best,
--Peter K1PO
Tom W8JI
wrote:
>>By the time we are done with all that fussing around, we might as well
>>buiild a good choke balun and put it on the output.
>
>Cannot really judge because I never did measurements on such an output balun but
>my feeling tells me that on some situations the influence of the balun can be
>disturbing and even give considerable losses and asymmetry. ( low Z and high
>reactive loads or on High Z/High reactive load's?)
Not actually. Draw it on paper and look at it.
If you use a floating network, and a choke balun, the common-mode
voltage across the balun is virtually the same no matter what side of
the network the balun is on. Since the isolation for common mode
voltage is what balances the line, moving the choke balun does noting
for balance. As a matter of fact, it probably makes it worse.
If you can find the web site URL, athat would be nice. I am not aware
of anyone using an isolation transformer...but I agree a transformer
belongs on the input of a tuner.
73 Tom
CAM
> A link in the wrong situation can increase common mode currents on a
> line, just as a balun in the wrong situation can increase common mode
> currents. We have to look at the exact situation.
That's exactly why I think your assertion that there cannot exist
a link between the differential impedance and the common-mode
currents is false.
CAM
> If the common modes are completely unobservable and uncontrollable from the
> differential modes and vice versa then, and only then, are the mode
> sub-systems independent. Comments, thoughts?
Seems to me, if they are completely independent, then installing
a balun is futile. Yet the same person who says they are independent
recommends installing a balun. Go figure.
Bill Russell
question!!! I can see that a lot of u folks know more about antenna
tuners than Ill ever understand. I think most hams are like
myself....ie: we know enough about antennas and tuners to get some
sort of signal on the air but thats about it. As far as my origonal
post goes, my intent is to used a 130 ft dipole center fed with window
line and use this antenna for all bands.....80 thru 10. I will be
using full power when needed. The reason for the question was 2
fold....1, i have read that using a balun at the output of the tuner
is not the best way to balance the output because of the different
loads it will see at different frequencys. Some manufactures put the
balun at the input of the tuner (Im thinking of the Palstar) to solve
this problem. With the balun at the input, when the tuner is tuned
correctly, the balun will always see the correct match regardless of
the frequency. The Johnson Match Box I believe used a link for this
purpose, no balun needed. 2, I want to be sure that the voltages and
currents are equal on both legs of the feed line so that the feed line
will not radiate. This is a function of the first part of my question
I think. People have mentioned the limitations of the Johnson Matchbox
and I agree. Since Im not interested in 160, that limitation is not a
problem. Having used a KW matchbox in the past, I found it is a little
more sensitive to feed line length and that "pruning" the feedline is
a little more critical. Anyway as I asked, why is everyone using a
balun today and not the link as Johnson did.
Thanks to all for you posts............Its back to the books for me so
I can understand what the hell your talking about!!!!! :)
Bill Russell
KC2IFR
Peter O. Brackett
[snip]
> Anyway as I asked, why is everyone using a
> balun today and not the link as Johnson did.
> Bill Russell
> KC2IFR
[snip]
Today, no commercial tuners use "link coupling" to achieve the balun
function simply because the more common modern torroid current baluns are
mechanically and electronically more *robust* and are commercially available
at feasible pricing to the manufacturers. Simply link coupling is not used
simply for manufacturing and packaging *build it for a buck* reasons. Open
air links bring along *packaging* problems that dissappear with the use of
torroids and other modern methods.
Link coupling will certainly do the job, it's simple, elegant, and
beautiful, but physically and economically just not as convenient in the
modern world.
It seems that the only way to avail oneself of link coupling today is to
"roll your own". Not a bad idea, eh?
--Peter K1PO
avatar
single ended tuner network.
There are those who believe the balun should be on the output of the tuner
and others who say it should be on the input of the tuner. Even with the
balun on the input a single ended tuner will work well with a balanced
feedline IF the tuner network components are floating above ground. Only the
ground side of the balun is connected to chassis ground.
Dave
W0MAY
Peter O. Brackett <ab...@ix.netcom.com> wrote in message
news:9ol2t3$t6l$1...@slb4.atl.mindspring.net...
Tom W8JI
wrote:
>That's exactly why I think your assertion that there cannot exist
>a link between the differential impedance and the common-mode
>currents is false.
but not nearly as wrong as saying there is a direct link. ;-)
73 Tom
Tom W8JI
<wi...@global2000.net> wrote:
>Wow.........i did not expect all the responces to my origonal
>question!!! I can see that a lot of u folks know more about antenna
>tuners than Ill ever understand. I think most hams are like
>myself....ie: we know enough about antennas and tuners to get some
>sort of signal on the air but thats about it. As far as my origonal
>post goes, my intent is to used a 130 ft dipole center fed with window
>line and use this antenna for all bands.....80 thru 10. I will be
>using full power when needed.
Part of the reason regular T network tuners get such a bad name is
virtually all manufacturers greatly over-rate the tuners for power.
This stems from the fact tuners were rated to match amplifier ratings
(dc input power) on 80-10 meters prior to the time when we started
talking about output power.
Only a few tuners rate by true output power.
To make matters worse, manufacturers and handbooks virtually never
gave proper operating instructions and most people were clueless about
how to *properly* tune a tuner without help, although that is
changing.
>The reason for the question was 2
>fold....1, i have read that using a balun at the output of the tuner
>is not the best way to balance the output because of the different
>loads it will see at different frequencys.
That is mostly a myth or incorrect assumption, although it is a
popular myth.
Moving the balun to the output does NOT improve balance or lessen
impedance requirements for a balun when the network is a floating
network that is not ground referenced.
>Some manufactures put the
>balun at the input of the tuner (Im thinking of the Palstar) to solve
>this problem. With the balun at the input, when the tuner is tuned
>correctly, the balun will always see the correct match regardless of
>the frequency.
It only sees the correct differential mode impedance, which has
nothing to do with balance and is the easiest problem to solve in
balun design.
>The Johnson Match Box I believe used a link for this
>purpose, no balun needed. 2, I want to be sure that the voltages and
>currents are equal on both legs of the feed line so that the feed line
>will not radiate.
Then you do not necessarily want the Johnston circuit, because it
ground references the feedline and feeds it with push-pull voltages.
Also the layout is somewhat non-symmetrical.
It does not force equal currents.
>problem. Having used a KW matchbox in the past, I found it is a little
>more sensitive to feed line length and that "pruning" the feedline is
>a little more critical. Anyway as I asked, why is everyone using a
>balun today and not the link as Johnson did.
Because out of all circuits, a C-L-C T network has the widest
impedance matching range over the widest frequency range for the least
cost, and a simple properly designed choke balun on the output makes
sure the currents are balanced in more practical applications.
All of my KW Matchbox's are in the storage barn, and I use ATR30's
which have better balance and handle more power with higher
efficiency.
>Thanks to all for you posts............Its back to the books for me so
>I can understand what the hell your talking about!!!!! :)
Just be sure the books or reference information is correct!
73 Tom
Tom W8JI
>and others who say it should be on the input of the tuner. Even with the
>balun on the input a single ended tuner will work well with a balanced
>feedline IF the tuner network components are floating above ground. Only the
>ground side of the balun is connected to chassis ground.
...and it will have the same or better balance if you move the balun
to the output in that case.
73 Tom
CAM
> CAM <Cecil....@IEEE.org> wrote:
>>That's exactly why I think your assertion that there cannot exist
>>a link between the differential impedance and the common-mode
>>currents is false.
>
> but not nearly as wrong as saying there is a direct link. ;-)
My point is that I can *cause* common-mode currents
to increase by mistreating the balun. Wouldn't you
say that the energy in the common-mode currents originates
in the differential currents emerging from the transmitter
coaxial connector? Can you have common-mode currents without
first having differential currents?
CAM
> Part of the reason regular T network tuners get such a bad name is
> virtually all manufacturers greatly over-rate the tuners for power.
They also tend to over-rate the built-in baluns. They seem
to assume the balun will see its designed-for impedance.
Ian White, G3SEK
specific antenna/feedline/transmatch/balun/ground configuration.
In any given configuration, a particular set of impedances and currents
will all coexist - because they're all results of that particular
configuration. The false logic is to believe they are results of each
other.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
Richard Clark
wrote:
>Can you have common-mode currents without
>first having differential currents?
>--
>cheers, CAM
Hi Cecil,
This is the most common form of the problem, but it is not a
necessity.
Peter O. Brackett
[snip]
> Can you have common-mode currents without
> first having differential currents?
> --
> cheers, CAM
[snip]
Well probably not in amateur antenna applications, but for instance... in
telephone network "phantom" circuits, both the differential and common modes
are deliberately driven simultaneously with different signals.
Phantom circuits/paths are set up using two twisted pair transmission lines.
Three different communications paths are set up, two differential mode
paths, one on each twisted pair, and one common mode path using both pairs.
--Peter K1PO
Peter O. Brackett
[snip]
> They also tend to over-rate the built-in baluns. They seem
> to assume the balun will see its designed-for impedance.
> --
> cheers, CAM
[snip]
To exacerbate the situation, there are apparently no manufacturers who make
definitive quantitative specs available for their in-tuner baluns.
I wonder how many good tuner products are "ruined" by "skimpy baluns"?
Like a lot of other ham radio product marketing the byword seems to
be...Caveat Emptor.
--Peter K1PO
George, W5YR
complex!
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
George, W5YR
very lately a voltage balun at that) that alone is fair evidence that the
designers have little knowledge of or experience with typical amateur
tuned-line applications.
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
Reg Edwards
> In any given configuration, a particular set of impedances and
currents
> will all coexist - because they're all results of that particular
> configuration. The false logic is to believe they are results of
each
> other.
Ian, its not false logic.
In the network consisting of ground, transmitter, tuner, feedline,
antenna and everything else in the near field, there is only one
generator - the transmitter itself.
ALL volts and currents, anywhere you like in the network, are all
directly proportional to the generator voltage and current.
All so-called common mode and any other sort of mode volts and
currents are locked to each other by their direct and mutual
couplings.
The only way of reducing supposed undesirable currents in any part
of the network of lines and mtual couplings is to change the
relative impedances in the various parts of the network.
In many cases the effect of reducing an unwanted current is to
shift it to an another equally unwanted location such as further
along the feedline.
If it works - don't fix it !
---
Reg
CAM
> The false logic is to believe they are results of each other.
Hmmmmmm, can you have common-mode currents without differential
currents from the transmitter?
CAM
> CAM <Cecil....@IEEE.org> wrote:
>
>>Can you have common-mode currents without
>>first having differential currents?
> This is the most common form of the problem, but it is not a
> necessity.
What does a common-mode transmitter look like?
Richard Clark
wrote:
>Richard Clark wrote:
>
>> CAM <Cecil....@IEEE.org> wrote:
>>
>>>Can you have common-mode currents without
>>>first having differential currents?
>
>> This is the most common form of the problem, but it is not a
>> necessity.
>
>What does a common-mode transmitter look like?
Hi Cecil,
Like any other. Quite common.
Tom W8JI
wrote:
>Tom W8JI wrote:
>
>> CAM <Cecil....@IEEE.org> wrote:
>>>That's exactly why I think your assertion that there cannot exist
>>>a link between the differential impedance and the common-mode
>>>currents is false.
>>
>> but not nearly as wrong as saying there is a direct link. ;-)
>
>My point is that I can *cause* common-mode currents
>to increase by mistreating the balun. Wouldn't you
>say that the energy in the common-mode currents originates
>in the differential currents emerging from the transmitter
>coaxial connector? Can you have common-mode currents without
>first having differential currents?
>--
>cheers, CAM
The logic is getting pretty lame now Cecil!
73 Tom
Tom W8JI
wrote:
>Tom W8JI wrote:
>
>> Part of the reason regular T network tuners get such a bad name is
>> virtually all manufacturers greatly over-rate the tuners for power.
>
>They also tend to over-rate the built-in baluns. They seem
>to assume the balun will see its designed-for impedance.
>--
>cheers, CAM
Choke-type baluns operate over a very wide impedance range without
major problems. Many people over-rate potential problems with
choke-type baluns.
73 Tom
Tom W8JI
>Considering that almost all such tuners incorporate a 4:1 balun (and until
>very lately a voltage balun at that) that alone is fair evidence that the
>designers have little knowledge of or experience with typical amateur
>tuned-line applications.
That isn't true any longer George, although it is a good indicator a
person does not understand a problem if he thinks a 4:1 balun is
desirable in most applications.
Some manufacturers have been using choke-type baluns exclusively since
the early 80's.
73 Tom
CAM
> CAM <Cecil....@IEEE.org> wrote:
>>My point is that I can *cause* common-mode currents
>>to increase by mistreating the balun. Wouldn't you
>>say that the energy in the common-mode currents originates
>>in the differential currents emerging from the transmitter
>>coaxial connector? Can you have common-mode currents without
>>first having differential currents?
>
> The logic is getting pretty lame now Cecil!
I'm serious, Tom. Seems to me, not only are the common-mode
currents powered by the differential currents from the
average ham transmitter, the common-mode currents are
even phased-locked to the differential currents. That you
believe there is no relationship between them is amazing.
CAM
> CAM <Cecil....@IEEE.org> wrote:
>
>>Tom W8JI wrote:
>>
>>>Part of the reason regular T network tuners get such a bad name is
>>>virtually all manufacturers greatly over-rate the tuners for power.
>>>
>>They also tend to over-rate the built-in baluns. They seem
>>to assume the balun will see its designed-for impedance.
>
> Choke-type baluns operate over a very wide impedance range without
> major problems. Many people over-rate potential problems with
> choke-type baluns.
Unfortunately, most of the built-in baluns are not choke-type baluns.
Bill Aycock
to these two statements. As it is, they are in the same category as "I
got an S9+20 from him after I added the gizmo"
Which tuners does Cec mean with "most of the built-in Baluns", and which
ones does Tom mean with "some manufacturers" ?
Bill-W4BSG
CAM wrote:
>
> Unfortunately, most of the built-in baluns are not choke-type baluns.
> --
> cheers, CAM
>
Ian White, G3SEK
>Ian said -
>> In any given configuration, a particular set of impedances and
>currents
>> will all coexist - because they're all results of that particular
>> configuration. The false logic is to believe they are results of
>each
>> other.
>===============================
>Ian, its not false logic.
>
>All so-called common mode and any other sort of mode volts and
>currents are locked to each other by their direct and mutual
>couplings.
>
That is exactly what I meant by saying that all the currents "coexist".
When you energize the system, it is the system configuration that
creates all the relationships between the different currents.
It's certainly true that current in any part of an antenna is created by
direct and mutual couplings with any other part. But that coupling is
*mutual* - it goes both ways - so it's false logic to single out any one
set of currents as a cause and see another set as effects.
What Tom meant by "no direct link" was that you can't make any
generalizations about the effects of common-mode and differential-mode
currents on each other without *also* specifying the whole configuration
- because it's the configuration that determines how they interact.
Those different currents and modes "co-exist" in the most literal sense
of the word. They all exist together, because all of them are the
*effects* of the system configuration (and the transmitter).
>The only way of reducing supposed undesirable currents in any part
>of the network of lines and mtual couplings is to change the
>relative impedances in the various parts of the network.
>
Exactly - you change the configuration so that it doesn't support the
unwanted mode any more.
>In many cases the effect of reducing an unwanted current is to
>shift it to an another equally unwanted location such as further
>along the feedline.
>
And that's the kind of mistake we make if we try to "fix" the common-
mode current at one point without realising that we're actually changing
the whole configuration.
Richard Clark
wrote:
>Tom W8JI wrote:
>
>> CAM <Cecil....@IEEE.org> wrote:
>>>My point is that I can *cause* common-mode currents
>>>to increase by mistreating the balun. Wouldn't you
>>>say that the energy in the common-mode currents originates
>>>in the differential currents emerging from the transmitter
>>>coaxial connector? Can you have common-mode currents without
>>>first having differential currents?
>>
>> The logic is getting pretty lame now Cecil!
>
>I'm serious, Tom. Seems to me, not only are the common-mode
>currents powered by the differential currents from the
>average ham transmitter, the common-mode currents are
>even phased-locked to the differential currents. That you
>believe there is no relationship between them is amazing.
Hi Cecil,
The notion that they MUST be related is the greater problem. You have
properly isolated an instance, true, but that does not fully qualify
what Common Mode is (and offers only a partial subset as an incomplete
example).
Amateur radio problems of Common Mode are not wholly confined to those
instances where the transmitter is both the Differential and (by
extension) Common Mode source. This particular example, as common as
it may be, is NOT the general description and rarely very few in this
group describe the Common Mode circuit completely, or correctly.
This last problem of properly describing the circuit is the greater,
undiscussed issue - not its modality (which, if the circuit cannot be
described, the labeling of modality is an exercise in futility). Even
Peter's description of the telephone example is incomplete and leaves
out the most important component of the Common Mode: its common (or
reference)! This is particularly dangerous in that the description of
reference is ALWAYS front and center to the distinction between Common
Mode and Differential Mode.
CAM
> Which tuners does Cec mean with "most of the built-in Baluns"...
MFJ-949E, for instance.
Peter O. Brackett
I believe the "reference" to be the "Ground at the end of the Universe".
David Adams once showed me where the ITU's International Ground was
connected to it at the back of the restaurant there.
--Peter K1PO
"Richard Clark" <kb7...@home.com> wrote in message
news:de81rt8c2hmskvogg...@4ax.com...
Peter O. Brackett
[snip]
"Bill Aycock" <bay...@hiwaay.net> wrote in message
news:3BB09746...@hiwaay.net...
> Tom and Cecil- it would help (me, at least) is there were specifics tied
> to these two statements. As it is, they are in the same category as "I
> got an S9+20 from him after I added the gizmo"
> Which tuners does Cec mean with "most of the built-in Baluns", and which
> ones does Tom mean with "some manufacturers" ?
>
> Bill-W4BSG
[snip]
Current baluns versus voltage baluns...
The irony is that there is almost no "cost" difference between a voltage and
a current balun.
It's an example of one of those few instances, where intelligence is better
than money!
--Peter K1PO
Bill Aycock
look.
Bill-W4BSG
Roy Lewallen
>
> Current baluns versus voltage baluns...
>
> The irony is that there is almost no "cost" difference between a voltage and
> a current balun.
>
> It's an example of one of those few instances, where intelligence is better
> than money!
>
> --Peter K1PO
The only difference between a 1:1 voltage and current balun is the third
winding on the voltage balun. This can, incidentally, simply be cut to
make a 1:1 voltage balun into a current balun. But a 4:1 current balun
requires two non-coupled cores, while a 4:1 voltage balun requires only
one. So there is a cost -- and size -- difference between these two. I
think you might be able to make a 4:1 current balun on a single two-hole
core by arranging the windings to minimize or cancel mutual flux, but
haven't really looked into it.
Roy Lewallen, W7EL
Bill Aycock
have made for myself have been current types.
But- this exchange is letting me learn a lot of colateral things.
Now- if I can get "input end" and "output end" straight- ( depends on
where you're standing, doesn't it? listening or talking.)- I'll be
happier. Why cant they say- "Transmitter end" and "antenna end" ?
Bill-W4BSG
Peter O. Brackett
Heh, heh...meaningful labels on windings.. that's an old problem, still with
us.
Even with digital interfaces like RS232, one man's Tx Data is another man's
RxData.
Back when I was in the business of manufacturing ferrite inductors,
transformers, hybrids, termination sets, equalizers, directional couplers,
etc... just to keep all the windings straight we used to label them "start"
and "finish", in manufacturing, and paint the ends with different colors,
but once the windings were in place it always seemed to me those "labels"
were meaningless and we ought to re-label them, to say "inside" and
"outside" or "1" and "2" or whatever...
Regardless of the labels on them, it's important to keep track of them as
you have noted.
A rose by any other name!
--Peter K1PO
"Bill Aycock" <bay...@hiwaay.net> wrote in message
news:3BB0D348...@hiwaay.net...
Ian White, G3SEK
>Ian White, G3SEK wrote:
>
>> The false logic is to believe they are results of each other.
>Hmmmmmm, can you have common-mode currents without differential
>
>currents from the transmitter?
On a two-wire transmission line, probably not. But that still doesn't
mean that either one is the result of the other.
If you know either current, you cannot predict the other one without
knowing about the total antenna/feedline/transmatch/ground
configuration. That is because they are both determined by the
configuration - not by each other.
Tom W8JI
<g4fgq...@btinternet.com> wrote:
>Ian said -
>> In any given configuration, a particular set of impedances and
>currents
>> will all coexist - because they're all results of that particular
>> configuration. The false logic is to believe they are results of
>each
>> other.
>===============================
>Ian, its not false logic.
>
>In the network consisting of ground, transmitter, tuner, feedline,
>antenna and everything else in the near field, there is only one
>generator - the transmitter itself.
>
>ALL volts and currents, anywhere you like in the network, are all
>directly proportional to the generator voltage and current.
>
>All so-called common mode and any other sort of mode volts and
>currents are locked to each other by their direct and mutual
>couplings.
All common-mode currents and differential-mode and life eventually
comes from the sun.
That is the source of virtually all energy used to generate or support
all three.
Because of that, it is all locked together. If you extinguish the sun,
we won't need baluns.
73 Tom
J. Harvey
de VE1...@rac.ca /VE3
PS: *Douglas* Adams isn't it - he died recently...
Tom W8JI
wrote:
>I'm serious, Tom. Seems to me, not only are the common-mode
>currents powered by the differential currents from the
>average ham transmitter, the common-mode currents are
>even phased-locked to the differential currents. That you
>believe there is no relationship between them is amazing.
>--
>cheers, CAM
My 75-meter dipole feedline has significant common-mode currents from
my 160-meter transmitter, while the differential mode excitation is
nearly zero.
A small loop antenna has nearly zero common mode currents at the
antenna despite lacking a balun, while the differential mode currents
are very very high.
A regular dipole with the feedline leabving at right angles suspended
in air has maximum common-mode current 1/4 wl from the antenna when
the feedline is 1/4 wl long and grounded only at the transmitter, and
minimum common mode current 1/4 wl from the antenna when the feedline
is 1/2 wl long and grounded only at the transmitter. This is true no
matter what the SWR is.
There is no universal relationship at all between the differential
mode impedance and the common mode impedance, and it is a giant leap
of faith to assume feeding the antenna at a current pioint makes balun
requirements less taxing. As a matter of fact, it can be JUST the
opposite in many cases!
73 Tom
Tom W8JI
wrote:
>Tom and Cecil- it would help (me, at least) is there were specifics tied
>to these two statements. As it is, they are in the same category as "I
>got an S9+20 from him after I added the gizmo"
>Which tuners does Cec mean with "most of the built-in Baluns", and which
>ones does Tom mean with "some manufacturers" ?
Ameritron has NEVER used a voltage balun, even MFJ now mostly uses
current baluns and has for several years. The only reason there isn't
more switch-over is because some people unwisely demand 4:1 baluns in
tuners or externally to use with open wire lines.
Any of the voltage baluns in use are VERY easily converted to current
baluns by moving two wires, most work significantly better that way.
73 Tom
Bill Aycock
a "pin-down" question- since the MFJ986 falls in an odd category, so far
as timing is concerned- does it have a voltage or a current Balun?
I ask, because the diagrams in the MFJ tuner manuals have a significant
number of drafting errors, and I'm not ready to take mine apart this
month, to check it out. (It's under other gear that would have to be
moved.)
Thanks- Bill-W4BSG
CAM
> CAM wrote:
>>Hmmmmmm, can you have common-mode currents without differential
>>currents from the transmitter?
>
> On a two-wire transmission line, probably not. But that still doesn't
> mean that either one is the result of the other.
Forgive me, Ian, but I cannot help but chuckle. Given that the only
source of power in the average ham's installation is the differential
current output of a transmitter, doesn't the differential current
cause lead to the common-mode result? Last time I checked, if one
turns off the power to the differential mode transmitter, the
common-mode current(s) disappear(s). IMO, if you know *all* the
characteristics of a particular antenna system, the common-mode
currents are perfectly predictable given the differential mode
current inputs.
This is, of course, assuming only one non-negliglible differential
source in the antenna system network.
CAM
> All common-mode currents and differential-mode and life eventually
> comes from the sun.
Cop-out! :-)
CAM
> There is no universal relationship at all between the differential
> mode impedance and the common mode impedance, and it is a giant leap
> of faith to assume feeding the antenna at a current pioint makes balun
> requirements less taxing. As a matter of fact, it can be JUST the
> opposite in many cases!
Let's talk about a typical ham installation - one differential
transmitter, one transmission line, and one dipole. Given no
other non-negliglible sources, the common-mode currents are
caused by the differential currents and are phase-locked to the
differential currents. It is a truism that baluns perform their
function best when their designed-for parameters are met. Have you
read, "Baluns: What They Do And How They Do It"? If proper attention
is paid to the physical geometry of the single antenna system, we
don't have to worry much about inducted common-mode currents. Conducted
common-mode currents seem to be pretty predictable and thus fairly
easy to eliminate with chokes assuming the chokes are working into
their designed-for parameters which is usually 50 ohms or close to
a current maximum point.
CAM
> Tom- and Cecil- You have been most helpful. The specifics do help. Now-
> a "pin-down" question- since the MFJ986 falls in an odd category, so far
> as timing is concerned- does it have a voltage or a current Balun?
Quoting the MFJ catalog, the MFJ986 has a "TrueCurrentBalun".
My older MFJ989 had a 4:1 voltage balun.
Roy Lewallen
common mode and differential mode currents are really mathematical
constructs. On a twin lead conductor, there are only two currents, one
on each wire. Neither is the common mode or differential mode current.
"Creation" of common mode current is done by disturbing the balance
between the two currents, that is, making them deviate from being equal
in magnitude and opposite in direction.
When coax is used, three currents are possible: one on the outside of
the inner conductor, one on the inside of the outer conductor, and one
on the outside of the outer conductor. Unlike the case with twin lead,
these can be identified as being purely differential mode current (the
currents on the inside) and common mode current (the current on the
outside). But remember that the fields on the inside don't appear on the
outside or interact with the fields on the outside, and vice versa.
It might be useful to keep these facts in mind when discussing common
and differential mode currents and their relationship.
Roy Lewallen, W7EL
George, W5YR
don't use it, preferring to use W2DU baluns to transition my ladderlines to
coax.
72/73, George W5YR - the Yellow Rose of Texas QRP-L 1373 NETXQRP 6
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe SOC 262
Amateur Radio W5YR, in the 56th year and it just keeps getting better!
Icom IC-756PRO #02121 Kachina #91900556 IC-765 #02437
Peter O. Brackett
"J. Harvey" <JM001....@sympatico.ca> wrote in message
news:gC7s7.20965$GQ2.1...@news20.bellglobal.com...
Peter O. Brackett
Ah yes, I believe that you'r correct it was Douglas not David, and I do
recall hearing of his untimely death.
I love the whole concept of the restaurant at the end of the Universe. It
all makes such sense.
--Peter K1PO
"J. Harvey" <JM001....@sympatico.ca> wrote in message
news:gC7s7.20965$GQ2.1...@news20.bellglobal.com...
Peter O. Brackett
[snip]
>On a twin lead conductor, there are only two currents, one
> on each wire. Neither is the common mode or differential mode current.
> "Creation" of common mode current is done by disturbing the balance
> between the two currents, that is, making them deviate from being equal
> in magnitude and opposite in direction.
>
> When coax is used, three currents are possible: one on the outside of
> the inner conductor, one on the inside of the outer conductor, and one
> on the outside of the outer conductor. Unlike the case with twin lead,
> these can be identified as being purely differential mode current (the
> currents on the inside) and common mode current (the current on the
> outside). But remember that the fields on the inside don't appear on the
> outside or interact with the fields on the outside, and vice versa.
>
> It might be useful to keep these facts in mind when discussing common
> and differential mode currents and their relationship.
>
> Roy Lewallen, W7EL
[snip]
I disagree.
In any differential transmission system there is an outbound and an inbound
path for differential current. There will be a differential current
outbound, call it I1, and a differential current inbound, call it I2.
If there is an unbalance such that the magnitude of I1 is not equal to the
magnitude of I2, then there must exist yet another non-zero current, this is
called the common mode current, denote it Ic. Ic will have the value:
Ic = (I1 + I2)/2. For example if I1 = 5.002A and I2 = -5.000A, then the
common mode current is Ic = 0.002A.
This Ic is a real current and it too must have an outbound and an inbound
path. It must return to the generator somehow. The paths or conductors
over which Ic flows are not always readily apparent, since usually no one
puts those paths on the schematic drawings, heh, heh.
Nonetheless Ic has to flow over/on conductors in the system somewhere!.
If the two opposite flowing currents in twin lead are not equal in magnitude
then there *is* a real third current Ic just as there is with coax. What may
be perplexing, to some, is that the conductor for the return of this third
common mode current Ic is never illustrated on the schematic diagram. Out
of sight out of mind they say! Schematic diagrams usually do not show the
outside of the coax as a separate conducting path, it's just never shown.
In fact, even with coax, not all of the common mode current is requried to
flow on the outside of the coax, it too may seek other paths not shown on
the schematic diagram just as in the case of twin lead.
The question is... what and where are the conductors on/in which the common
mode current flows?
The answer(s) to those questions are what separates the differential mode
boys from the common mode men.
--Peter K1PO
Peter O. Brackett
[snip]
> Quoting the MFJ catalog, the MFJ986 has a "TrueCurrentBalun".
> My older MFJ989 had a 4:1 voltage balun.
> --
> cheers, CAM
[snip]
Heh, heh... I love Martin's marketing jargon.
I wonder what the difference is between a "True" current balun and just a
plain vanilla current balun.
--Peter K1PO
PS: I consider Martin to be a good friend, and one of the most astute
businessmen I know.
Peter O. Brackett
Maybe y'all are onto something here!
[snip]
"George, W5YR" <w5...@att.net> wrote in message
news:3BB14EBC...@att.net...
> My MFJ 989C purchased about 4 years ago claims to have a current balun. I
> don't use it, preferring to use W2DU baluns to transition my ladderlines
to
> coax.
>
> CAM wrote:
>
> > Quoting the MFJ catalog, the MFJ986 has a "TrueCurrentBalun".
> > My older MFJ989 had a 4:1 voltage balun.
[snip]
*Note to Martin Jue*
There appears to be an untapped opportunity in the antenna tuner market
segment.
There appears to be an unsatisfied demand for antenna tuners with plug in
baluns!
Just provide a trapdoor and socket for plug in baluns on the tuners and then
market a line of "plug in baluns".
That way everyone can go to hell there own way!
-Peter K1PO
Rick Littlefield
differential
current output of a transmitter, doesn't the differential current cause lead to
the common-mode result?<
Alas, once again, good science falls victim to rhetorical foible and shoots
itself in the ass.
Looking at Cecil's premise, I'd say "cause" and "lead to" might constitute the
fly in the pie.
Another good fight over a bad premise.
Rick K1BQT
Ian White, G3SEK
>Ian White, G3SEK wrote:
>
>> CAM wrote:
>>>Hmmmmmm, can you have common-mode currents without differential
>>>currents from the transmitter?
>>
>> On a two-wire transmission line, probably not. But that still doesn't
>> mean that either one is the result of the other.
>
>Forgive me, Ian, but I cannot help but chuckle. Given that the only
>source of power in the average ham's installation is the differential
>current output of a transmitter, doesn't the differential current
>cause lead to the common-mode result? Last time I checked, if one
>turns off the power to the differential mode transmitter, the
>common-mode current(s) disappear(s).
Of course it does, but I mean no discourtesy by calling that a 'trivial'
observation - one that is perfectly obvious but provides no further
information. Slightly more useful, but still trivial, is that the
differential and common-mode currents in a given system will scale in
linear proportion to each other.
>IMO, if you know *all* the
>characteristics of a particular antenna system, the common-mode
>currents are perfectly predictable given the differential mode
>current inputs.
>
That is true, because they are locked together by the way that the "laws
of physics" act upon the antenna system. However, it is equally true
that if you know the system and its common-mode currents, you can
predict the differential-mode currents. But if you don't know the
system, you cannot predict either one from the other.
What you have there is a set of scrappy generalizations that only show
you parts of the picture, or else don't always work.
The big picture is that the system creates both the common-mode and
differential-mode currents at the same time. That is a better viewpoint
because it always works. If you want to change either of those currents,
think about what you have to do to the system to get what you want.
Picking up Roy's point, when a program such as EZNEC predicts unequal
currents on two parallel wires, it's conventional to resolve them into
common and differential modes because that's a more useful viewpoint.
They are "twinned results", both coming out of the same mathematical
operation at the same time - neither one is "senior" to the other as
Cecil seems to believe.
Tom W8JI
wrote:
>don't have to worry much about inducted common-mode currents. Conducted
>common-mode currents seem to be pretty predictable and thus fairly
>easy to eliminate with chokes assuming the chokes are working into
>their designed-for parameters which is usually 50 ohms or close to
>a current maximum point.
Common mode current or voltage levels are not directly related to
differential mode impedance of a system. They are two entirely
different things.
Choking type-baluns are designed for common mode impedance, and care
less about the normal differential mode impedance on the line unless
the wire itself would fail. If that was the case, it would fail
whether in a balun application opr a normal transmission line
application.
It is very misleading to say choke baluns (current baluns) have to be
operated at a certain "design impedance".
73 Tom
Tom W8JI
>My MFJ 989C purchased about 4 years ago claims to have a current balun. I
>don't use it, preferring to use W2DU baluns to transition my ladderlines to
>coax.
The balun in the tuner is actually much better for the application,
because the common mode impedance is much higher over a wider range
and it dissipates less power for a given common mode current.
73 Tom
CAM
> Common mode current or voltage levels are not directly related to
> differential mode impedance of a system. They are two entirely
> different things.
Saying the same thing over and over does not make it true, Tom.
I say, in the average amateur radio antenna system, the differential
currents and the common-mode currents are so closely related that
they are phase-locked and that if *all* system parameters are known,
they are both perfectly predictable. You apparently subscribe to
Plato's principles of reality (nothing can be known for certain)
while I subscribe to Aristotle's reality (a thing is what it is).
> Choking type-baluns are designed for common mode impedance, and care
> less about the normal differential mode impedance on the line unless
> the wire itself would fail.
So you disagree with, "Baluns: What They Do And How They Do It"?
> It is very misleading to say choke baluns (current baluns) have to be
> operated at a certain "design impedance".
If a choke balun has no design parameters at all, why bother with a
balun? (which I know you do bother with) If design parameters don't
matter, why is ten turns superior to one turn?
--
cheers, CAM, W5DXP
CAM
> The balun in the tuner is actually much better for the application,
> because the common mode impedance is much higher over a wider range
> and it dissipates less power for a given common mode current.
If the differential impedance doesn't matter, why does the common-
mode impedance matter? The original differential current has to choose
between the preferred common-mode path and the unwanted common-mode path.
Doesn't that suggest that the preferred common-mode path impedance should
be made low and the unwanted common-mode path impedance should be made high?
Or can we just forget trying to choke anything because everything is
completely unrelated and unknowable?
--
cheers, CAM, W5DXP
Rick Littlefield
and the common-mode currents are so closely related that they are
Which is the locker and which is the lockee???
Rick K1BQT
Tom W8JI
wrote:
>Tom W8JI wrote:
>
>> Common mode current or voltage levels are not directly related to
>> differential mode impedance of a system. They are two entirely
>> different things.
>
>
>Saying the same thing over and over does not make it true, Tom.
I agree, so I wish you would quit with the nonsense that common mode
stress of a balun is related to differential mode stress.
It is very misleading.
73 Tom
CAM
> Which is the locker and which is the lockee???
The source is the source.
CAM
> I agree, so I wish you would quit with the nonsense that common mode
> stress of a balun is related to differential mode stress.
I ask you once again: Is the information in "Baluns: What They
Do And How They Do It" incorrect?
If common mode currents are random and unrelated to the differential
current source, then wouldn't putting a choke in the refrigerator
work just as well as putting it on the antenna system?
Tom W8JI
wrote:
>I ask you once again: Is the information in "Baluns: What They
>
>Do And How They Do It" incorrect?
I don't know, I've read enough about baluns over the years and made
enough measurements I have no interest in reviewing or reporting on
other articles.
>If common mode currents are random and unrelated to the differential
>current source, then wouldn't putting a choke in the refrigerator
>work just as well as putting it on the antenna system?
Quit being being Chipish. You know better than that.
Differential mode impedance is an entirely different mode and
"circuit" than common mode impedance. Virtually everyone agrees on
that.
Just because we make the across voltage minimum from conductor to
conductor it does not mean we did that with the voltage that would be
across the longitudinal impedance of a balun doing it's job.
73 Tom
J. Harvey
> Quit being being Chipish.
Ohhhh... ..low blow !
I believe that your two arguments are mutually orthogonal. I'm not going to
even attempt to paraphrase them to make that claim clear. Perhaps you could
each paraphrase your own points to see if my hypothesis is correct.
Best wishes.
de VE1...@rac.ca /VE3
Peter O. Brackett
[snip]
>
> Just because we make the across voltage minimum from conductor to
> conductor it does not mean we did that with the voltage that would be
> across the longitudinal impedance of a balun doing it's job.
>
> 73 Tom
[snip]
Come on Cecil, you know that Tom is right!
Signal correlation bears no relationship to impedance levels in the common
and differential mode systems. Impedance levels are simply parameters of
the physical circuit and have nothing to do with the generators.
Although, as you have noted, in most amateur antenna applications it is true
that the common mode and differential mode signals are correlated, it is not
true that the common mode impedance levels at any particular point in an
antenna system are correlated to the differential mode impedance levels
nearby.
Common mode choke effectiveness must be measured against the prevailing
common mode impedance not the local differential mode impedance.
What?
--Peter K1PO
CAM
> Differential mode impedance is an entirely different mode and
> "circuit" than common mode impedance. Virtually everyone agrees on
> that.
I never said it wasn't a different mode. It is a different mode by
definition. What I said is that I can cause common-mode currents to
change by changing the differential-mode impedance. I proved that to
be the case today. I set up a 50 ohm center-tapped dummy load driven
by a 1:1 current balun and measured the common-mode current. It was
minimum. I disconnected one end of the center-tapped dummy load. The
common-mode current went sky high. I also proved that the differential
currents and common-mode currents are related. I disconnected the coax
connector at the transmitter differential output and the common-mode
currents went to zero.
This started out as a joke, Tom. Common-mode currents and differential-
modes currents *are* related in the ordinary single differential output
amateur transmitter system driving a single antenna. The differential-
mode currents are one of the causes of common-mode currents.
Consider a one second long 50 ohm coaxial transmission line. There will
not be any common-mode currents for one second after the transmitter is
keyed. To say common-mode currents are unrelated to differential-mode
currents is ridiculous.
CAM
> Common mode choke effectiveness must be measured against the prevailing
> common mode impedance not the local differential mode impedance.
Today I changed the local differential mode impedance and *caused*
the common-mode current to jump by a couple of magnitudes.
EZNEC displays common-mode currents. When I take away the differential
source, the common-mode currents disappear. When I re-install the
differential source, the common-mode currents assume exactly the same
value as they had before. If common-mode currents are random and
unpredictable, why does EZNEC display the same value time after time?
Maybe Roy needs to add a random number generator to the common-mode
current display?
CAM
> I believe that your two arguments are mutually orthogonal. I'm not going to
> even attempt to paraphrase them to make that claim clear. Perhaps you could
> each paraphrase your own points to see if my hypothesis is correct.
OK, here's mine. In the ordinary single differential mode transmitter
plus single antenna system, when you turn off the differential current
source, the common-mode currents disappear, i.e. they are related.
J. Harvey
> OK, here's mine. In the ordinary single differential mode transmitter
> plus single antenna system, when you turn off the differential current
> source, the common-mode currents disappear, i.e. they are related.
Sounds pretty controversial to me ! NOT ! ;-)
But...
Let's turn the power back on, everything steady state, with an imperfect
dipole fed with coax, CW, brick on the key. Now someone goes out in the
back yard and starts flapping the feedline back and forth like a crazy
vertical skipping rope.
Do things change ?
CAM
>> Let's turn the power back on, everything steady state, with an imperfect
> dipole fed with coax, CW, brick on the key. Now someone goes out in the
> back yard and starts flapping the feedline back and forth like a crazy
> vertical skipping rope. Do things change ?
They may change, but they are still phase-locked. And if the changes
can be properly modeled, they can be proven not to be random. If
everything is known about the system, everything is perfectly
predictable, i.e. there are no supernatural occurrences and
all the parameters obey the laws of physics. No Witch Doctor
is needed to explain things to us mere mortals.
Roy Lewallen
currents. A common mode current is half the sum of two different
conductor currents. EZNEC doesn't calculte this sum nor does it display
it. Likewise, a differential mode current is half the difference between
two currents. EZNEC doesn't display these either. If you want to know
the value of a common mode or differential mode current, you'll have to
first decide which two currents you want to use for the calculation,
then do the calculation yourself.
Roy Lewallen, W7EL
J. Harvey
> They may change, but they are still phase-locked.
> And if the changes can be properly modeled, they
> can be proven not to be random. If everything is
> known about the system, everything is perfectly
> predictable, i.e. there are no supernatural
> occurrences and all the parameters obey the laws
> of physics. No Witch Doctor is needed to explain
> things to us mere mortals.
Well, the one spinning the feedline is actually Schrodinger's Cat after a
particularly heavy meal of catnip laced with just a bit of uranium. The cat
might be dead or the cat might be alive. The feedline just sort of
disappears into the sealed box. We just don't know what to expect. Sorry -
I'm drifting...
Anyway, most arguments about physics (and many other topics as well) are
actually just arguments about the exact meaning of words - and usually it
isn't the complicated words - just simple ones like "related". The physics
is well known and agreed by all.
People are all too quick to assume that the disagreement is caused by
someone else's misunderstanding of physics. when actually it is quite often
just slightly different definitions. Many words have so many definitions and
shades of meaning.
I suspect in this case, everybody understands the physics just fine. The
only difference might be wording of the statements - people are reading them
different than intended. I'm sure with a few more hours of debate you could
all issue a "Joint Communiqué" that would cover the topic explicitly and
would be acceptable to all concerned.
Jeffrey (<-means peacemaker) Harvey
VE1...@rac.ca /VE3
Ian White, G3SEK
>Peter O. Brackett wrote:
>
>> Common mode choke effectiveness must be measured against the prevailing
>> common mode impedance not the local differential mode impedance.
>Today I changed the local differential mode impedance and *caused*
>
>the common-mode current to jump by a couple of magnitudes.
>
>EZNEC displays common-mode currents. When I take away the differential
>source, the common-mode currents disappear. When I re-install the
>differential source, the common-mode currents assume exactly the same
>value as they had before. If common-mode currents are random and
>unpredictable, why does EZNEC display the same value time after time?
Dammit, Cecil, nobody except you said they are either random or
unpredictable. You invented that all by yourself.
It's simply that the relationship depends on the entire system.
"Baluns - What They Do, etc" shows that very clearly.
Peter O. Brackett
[snip]
> To say common-mode currents are unrelated to differential-mode
> currents is ridiculous.
> --
> cheers, CAM, W5DXP
[snip]
Roger that!
But that being said, it is still true that common mode impedances are in
general not well related to differential mode impedances.
BTW Cecil, when didja get the new "DXP" call?
--Peter K1PO